Accumulative Roll Bonding of Aluminium
Table of Contents
II. Roll Bonding4
II.1. Surface Preparation4
II.2. Bonding Mechanism5
II.3. Roll Bonded Materials and Applications6
III. Accumulative Roll Bonding7
III.1. Introduction to Severe Plastic Deformation (SPD) Processes7
III.2. Accumulative Roll Bonding (ARB) Process8
III.3. Accumulative Roll Bonded Materials10
III.4. Material Structure after Accumulative Roll Bonding11
III.5. Mechanical Properties after Accumulative Roll Bonding13
III.5.1. Strength and ductility13
III.6. Applications of Accumulative Roll Bonding Process16
III.6.1. Manufacturing of a Cu/Al2O3 composite16
III.6.2. Manufacturing of nanostructure Al/SiCp Composite17
Research in severe plastic deformation (SPD) processes has increased a great deal over the last ten to fifteen years. Accumulative roll bonding is a radical, new (1998) process with limitless capabilities. Rolling is a process which has been used for a long time in almost all the steel mills around the world. The purpose of roll bonding is to combine two materials through rolling in order to achieve the desired mechanical properties.
This report intends to explore the evolution of the mechanical properties such as ductility, yield strength, ultimate tensile strength and hardness through grain refinement at the microstructural level. The mechanism of surface deformation, grain boundary deformation and reduction of work hardening is further analysed. This report also makes an effort to understand the accumulative roll bonding process as applied to aluminium and its alloys.
II. Roll Bonding
Roll bonding or also called roll welding is a cold welding process which is performed by the application of pressure on long pieces / strips through a pair of rolls. The process can be performed by application of heat or otherwise (Kalkpakjian et al. 2009, p760). To perform roll bonding, the material should satisfy certain characteristics which are ductility and crystallographic structures. Firstly, in roll bonding, at least one or both of the materials should have superior ductile properties (Kalpakjian et al. 2011, pp819-820). The reason for this is that if the material is not ductile, the failure would occur at a sooner stage of the plastic deformation and therefore, the bonding would not occur. Secondly, with respect to crystallographic structures, for the roll bonding of two different materials, the difference in the atomic radius should be less than 15% and the two metals should have the same crystal structures (Kalpakjian et al. 2011, p124).
Figure 1. roll bonding principle (Li et al. 2008, p2)
II.1. Surface Preparation
Before roll bonding, the work surfaces should be prepared. This is performed by degreasing, wire brushing and wiping in order to remove oxide layer (Kalpakjian et al. 2011, p820). In addition, it is also done by other chemical and mechanical treatment (Danesh et al. 2008, p2003). Indeed, it is really important to remove this oxide smudge firstly to avoid any corrosion problem which would occur during the part's lifetime and secondly, to increase the bond strength between the two materials (Movahedi et al. 2007, p417). II.2. Bonding Mechanism
More specifically, in roll bonding, the establishment of the atomic bond happens between decontaminated areas. During the rolling operation, the surface layers which are in contact with each other break-up and the underlying layers of the components extrude through the cracked layers. The bond strength between the two materials is dictated by parameters such as material thickness, surface preparation method, surface roughness, time taken between surface preparation and rolling, rolling temperature, reduction of thickness during rolling, rate of deformation and heat treatment after bonding...